An image generation device is known in the art for disposing a plurality of objects within an object space, which is a virtual three-dimensional space, and generating an image as seen from a given viewpoint within that object space, making it highly popular for enabling players to experience a virtual reality. With such an image generation system, it is desirable to generate realistic images to enhance the player's sensations of experiencing a virtual reality.
Incidentally, various different animation films and images become popular. These fascinate people, not because they are close to reality, but because they enable people to enjoy cel-style images that are the domain of animation.
However, animation images are projected from a recreation of previously prepared animation cel images, so they can be used for movies and moving images for a game opening, but it has not been possible to use them for game images that change in real-time. Either slick images with shading produced by smooth shading methods or two-dimensional images with absolutely no shading are used for game images that change in real-time.
The present applicants have proposed and developed an image generation system that changes a cel animation type of image in real-time, in accordance with a player's input. In this case, there is a problem concerning what sort of shading should be applied to produce a cel animation type of image.
It is theoretically possible to vary a cel animation image in real-time by applying a cel animation style of rendering, and an animation shader is known as a method therefore. However, the animation shader method involved a heavy processing load, so it is difficult to apply it to a domestic or arcade game system in which real-time response is required.